Method of preparing pulverized molybdenum disulfide



United States Patent 3,082,065 METHOD OF PREPARING PULVERIZED MOLYBDENUM DISULFIDE Ernest S. Wheeler, Langeloth, Pa., assiguor to American Metal Climax, Inc., New York, N.Y., a corporation of New York No Drawing. Filed July 11, 1960, Ser. No. 41,772

9 Claims. (Cl. 23-134) This invention pertains to a method of preparing molybdenum disulfide powder and more particularly, to an improved and simplified method of preparing an exceedingly fine molybdenum disulfide powder adapted for use as a dry lubricant or as an additive for greases, oils and the like and which powder is characterized by the presence of a controlled quantity of an oily substance. The oily substance provides a protective coating of the particles preventing oxidation thereof and may be controlled in amount to produce a seemingly dry molybdenum disulfide powder having substantially free flowing characteristics or can contain any desired greater quantity.

It is now known that dry and oil free molybdenum disulfide powder will oxidize on aging in the presence of air, forming oxides of molybdenum and sulfur which impart objectionable acidity to the powder. Acidity is particularly objectionable when the powder is to be used as a lubricant. The susceptibility of the molybdenum disulfide powder to oxidation is more pronounced when the particle size in the order of about five microns or less. This factor is significant because preferred powders have va degree of fineness of this magnitude. Moreover, while impact pulverization of the molybdenum disulfide powder in a fluid energy mill is an eflective way to achieve the desired fineness it is particularly conducive to the oxidation of the molybdenum disulfide particles both during and after the pulverizing operation.

In the past it has been proposed that the wet oily powdered molybdenite concentrate produced from molybdenite ore by successive grinding and flotation extraction processes be subjected to a controlled retorting operation to eliminate water and reduce the oil content to less than .5 so that the powder will flow freely. This material may then be pulverized in a fluid energy mill if finer powder is desired. However, this procedure requires relatively expensive retorting and retort controlling equipment.

Accordingly, it is a primary object of the present invention to provide an improved method of producing molybdenum disulfide powder having a controlled residuary oil content for oxidation inhibition that is simpler and more economical than methods heretofore known. Another object of this invention is to provide an improved method for producing finely powdered molybdenum disulfide requiring a minimum of processing steps and equipment whereby the residuary oil content and final particle size of the molybdenum disulfide product is simply and accurately controlled within desired limits.

The foregoing and other objects of this invention are achieved by charging molybdenum disulfide powder containing up to about 16% water and from about 1% to about 8% of an oily substance to a fluid energy impact pulverization mill and pulverizing the powder under controlled conditions to produce a substantially dry and exceedingly fine sized powder containing a controlled residuary oil content ranging from about 0.05 up to a content approaching that of the feed material, as desired.

Other objects and advantages of the present invention will become apparent from the following detailed description.

Commercial molybdenum disulfide has been produced in the past by grinding molybdenite ore which is comprised largely of granite containing molybdenum disulfide 3,082,065 Patented Mar. 19, 1963 and subsequently separating the molybdenum disulfide from the gangue by flotation extraction techniques employing oily materials of various kinds including petroleum oils. The extraction of the molybdenum disulfide from the molybdenite ore by the oil flotation process entails repeated grinding and flotation operations until the amount of gangue is reduced to the desired level. The gangue which is comprised predominantly of silica and is hereinafter referred to as such, is usually identified as the portion insoluble in nitric acid and soluble in hydrofluoric acid. In the usual commercial flotation extraction process the silica content of the molybdenum disulfide is reduced to a level below 12%. It is possible, however, in situations where a high silica content cannot be tolerated such as, for example in the case of a molybdenum di sulfide lubricant, to reduce the silica content of the extracted molybdenum disulfide to a level ranging from about 3% to about .5% by repeated or successive grinding and oil flotation extraction and during which the extracted molybdenum disulfide particles are reduced until essentially all are under 250 microns in size, with particles distributed down into the range of less than one micron. Further reduction of the silica content below a level ranging from about 3% to about .5 by successive grinding and oil flotation extraction is generally not economical in view of the comparative economics of alternate chemical leaching processes.

The percentage composition of the molybdenum disulfide powders as hereinbefore and hereinafter described,

unless otherwise specified, are expressed in terms of percentages by weight of the total mixture.

In accordance with the practice of the present invention num disulfide particles containing up to about 16% water and up to about 8% flotation oils. The residuary flota-' tion oil content in the extracted powder can be comprised of a wide variety of oily substances of a vegetable or petroleum origin and mixtures thereof which will wet the surfaces of the particles. Suitable oils for this purpose include refined petroleum oils, kerosene, pine tar oil, or-

any of the oily substances disclosed in United States Patout No. 2,686,156. It is preferable that the residuary oilcontent include some fairly high boiling point oils; for example, oils having an end boiling point of about 250 C. to facilitate control of any subsequent evaporation of the excess portion thereof in order to reduce the residuary oil content to a range within prescribed limits.

The wet, oily mass of extracted molybdenum disulfide powder can be charged directly to the impact pulverization mill and pulverized under controlled conditions wherein the water content is reduced to a level less than about 0.5% and the oil content is reduced to a level ranging from about 0.05% up to a level approaching the content of the feed stock, and preferably from about 1% to about 5%. An oil coating at a concentration as low as 0.05% will provide minimal protection of the MoS particles against oxidation. Higher oil concentrations provide still better protection and superior stability against oxidation. If desired, the extracted molybdenum disulfide powder prior to pulverization can be subjected to an intervening chemical treatment to reduce the silica content to a range of from about 0.01% to about 0.05% without significantly reducing the oil content. The wet, oily molybdenum disulfide powder whether or not subjected to the prior chemical treatment can be alternatively treated in a preliminary drying step wherein all or a substantial portion of the moisture is removed. The drying operation may be achieved by any one of a number of well known methods to evaporate water without reducing the 3 oil content significantly. Accordingly, the feed material to the fluid energy impact pulverization mill can comprise the wet, oily powdered mass derived directly from the oil flotation extraction operation or the oily powdered mass derived from the intervening chemical treating process and/or drying operation.

Comminution of the molybdenum disulfide powder A and controlled reduction of the residuary oil content is achieved in an impact pulverization mill in which the particle size is reduced by impactand abrasion of the individual particles against each other at high velocities while entrained in a stream of circulating gaseous fluid. The .fiuid mediumin which the feed particles are entrained as they enter the impact pulverization millcan be any compressed gas or vapor such as, for-example, air, CO nitrogen or superheated steam. Mills suitable for this purpose are made among others by Fluid Energy Processing and Equipment Company, of Philadelphia, Pennsylvania, and by Sturdevant 'Mil1'Co., of Boston, Massachusetts.

Impact pulverization, or micronization' as his usually referred to, can be controlled to produceproducts having various particle size distributions. Centrifugal action retains the heavier and/or larger particles within the mill for further milling and only the finer and/or 'desired sized particles are carried out as the product by the fluid stream. In the preferred practice of the present invention the extracted molybdenum disulfide particles charged to the impact pulverization mill 'are essentially all sized under 250 microns, with particles distributed down into the range of less than one micron. The particles are thereafter materially reduced in 'size until the size distribution and/or size range desired is obtained. Mo-

lybdenum disulfide powder having essentially all the par ticles under 5 microns in size is particularly desirable for dry lubricants or when compounding the powder with suitable lubricating oils and greases.

The residual oil content in the feed material provides excellent protection against oxidation duringthe impact pulverizing operation and also provides protection against oxidation for extended periods of time thereafter. The impact and abrasion between particles occuring during the impact pulverizing operation serves to substantially uniformly coat each of the particles and the freshly exposed surface area created by the breakdown of large particles into a plurality of smaller particles. The effectiveness of this coating mechanism is surprising in view of the fact that the direct coating of the powder with such small quantities of oil by ordinary mixing techniques is virtually impossible, and further, that the surface area of the powder is increased many times during pulverization. It is thought that in addition to the tendency of oil films to spread, the possible higher spot temperature at point of contact between particles may cause oil evaporation followed by immediate condensation, a part of which may be on the newly'produced oil-free surfaces. Another surprising feature is that oil film resulting from oil contents as high as -8% does not so cushion impact between the small particles as to reduce the efliciency of the mill. The relatively high efficiency realized is believed attributable to the fact that the feed material itself is of a relatively fine particle size, preferably less than about 250 microns, and in which form the feed material has a high surface area over which even relatively high oil contents can be distributed in substantially thin films.

The quantity of water and oil removed in the milling operation is controlled by controlling the temperature of the gaseous fluid, and the volume of gaseous'fluid per pound of molybdenum disulfide powder charged to the mill. As heretofore mentioned, the molybdenum disulfide feed material may comprise a wet, oily powder containing up to about 16% water. Rapid and efficient drying of the powder during the milling operation is faciliated by using heated air as the fluid. Separate milling runs conducted at air temperatures of 400 F. and 250 F. eliminated all but slight trace quantities of moisture in the final pulverized product. The drying effect increases as the temperature of the gaseous milling fluid increases. However, it has been observed that temperatures of about 900-1000 F. promote the oxidation of the molybdenum disulfide powder during impact pulverization and for this reason it is usually preferred to employ gaseous fluids at temperatures below this level. Thus, compressed air or other gases at temperatures preferably ranging from room temperature (about 65 F.) to about 700 F. may be used depending upon the drying effect or oil content desired. Alternatively, steam at a temperature up to about 750 F. can be employed as the milling fluid for vaporizing and removing the water and oil from the powder during the milling operation if such is desired. The milling operation is ordinarily effective to reduce the content of water to a level below about 0.5%. Although a water content of about .5% in the pulverized prodnct is not objectionable for certain uses it is preferred that the milling operation be conducted in a manner to remove essentially all of the moisture or to subject the powder prior to milling to a preliminary drying step as hereinbefore described.

Variations in the temperature of the milling fluid and the volume of fluid per pound of Mes charged to the mill not only effect the removal of moisture from the powder but also provide a control for removing a portion'of the residuary flotation oil content. As-the temperature of'the'fluid increases the quantity of residuary oil removed increases correspondingly. In'addition, the

amount of oil retained after milling is also dependent on the volatility characteristics of the residuary oil content and the quantity initially present. The micronization of a powder containing about 7% residuary flotation 'oil with air at a temperature of 400 F. and at a controlled feed rate resulted in a removal of from about 15% to about 46% of the initial oil content. The amount removed was reduced to about 8% when the same powder was milled with air at a temperature of about 90 F. At temperatures of 450 F. to 650 F, the percent oil removed has ranged from 6% to 80% depending on the .of the pulverized product.

temperature, air volume, and feed rate. From the foregoing it will be apparent that the desired residuary oil content in the powdered product can be established by trial for any given feed stock containing a given percentage of flotation oils having specified volatility characteristics. Where it is desired to retain a maximum quantity of the flotation oil in the micronized product it is preferred to conduct the milling at a low temperature of about F. preceded by a preliminary drying step of the irharged material so that the final water content will be There is evidence indicating that a reduction in the acidity of the feed material occurs during the impact pulverization operation producing a final product having a lower acidity than the feed material. The mechanism by which this is achieved is not completely understood but is believed that sulfur dioxide and sulfur trioxide entrapped among or adsorbed on the particles of the feed material are released during the pulverizing operation and thereafter removed by the propelling fluid in which the particles are entrained thereby reducing the acidity It was found that at milling temperatures above about 400 F. significant improvement in the reduction of the acid number of the micronized powder was obtained. Analyses made on a typical molybdenum disulfide powder derived directly from the flotation extraction process and micronized at a temperature above 400 F. indicates an acidity of less than 0.05 ml. N/ 10 KOH per 10 grams of the micronized powder. This reduction in the acidity of the molybdenum disulfide powder by the impact pulverization'operation constitutes another advantage of applicants unique method of preparing molybdenum disulfide powders.

' residuary oil content was 1.7%.

5 The simplicity-and effectiveness of the method comprising the present invention for producing a substantially dry, exceedingly fine molybdenum disulfide powder containing a controlled quantity of residuary oil is further illustrated by way of the following examples which are provided for illustrative purposes and are not intended to be limiting in any way.

EXAMPLE I A wet, oily mass of molybdenum disulfide powder derived directly from the oil flotation extraction process of powdered molybdenite ore and containing about 6% oil and 16% water was charged at the rate of 450 pounds per hour to a fluid energy impact pulverization mill. The molybdenum disulfide particles were pulverized while entrained in air heated to 600 F. at a pressure of 92 pounds per square inch and injected at a rate of 510 cubic feet per minute. During the pulverizing operation, samples of the pulverized powder product were periodically taken and analyzed for acidity, molybdenum oxide content, water content, residuary oil content, and particle size. The resultant molybdenum disulfide product was found to have an average acidity of .078 N/ 10 KOH per 10 grams of the powdered product. The molybdenum oxide content (M was .041%. The water content of the resultant powdered product was .057% while the Comminution of the feed material during impact pulverization progressed to the extent that the resultant powdered product had a particle size of 95% by weight less than 5 microns.

The efiectiveness of the oil content in the molybdenum disulfide powder to prevent or minimize oxidation thereof during the impact pulverization operation and for substantial periods of time thereafter is illustrated in the next example.

EXAMPLE -II A wet, oily mass of molybdenum disulfide powder derived from the oil flotation extraction process of powdered molybdenite ore was subjected to chemical treatment whereby the silica content was reduced to a level less than .5%. The resultant chemically treated powder which contained 16.3% water and 6.2% oil was divided into four aliquot portions designated as samples A, B,

Sample Sample Sample Sample A B C D Milling Conditions:

Air Temperature, F 575 640 550 445 Air Flow Rate, s.e.i=m 51 510 510 510 Air Flow Rate at Temp. c.f.m- 1,095 1, 060 975 880 Feed Rate, lbJhr 390 726 611 569 Composition of Micronized Product:

Oil content, percent.--" l. 2 2. 7 3. 3 5. 8 H1O content, percent. M001, percentat start 05 05 .05 .04 After 18 days.-. 04 04 04 04 After 49 days 03 04 .04 04 Atibd Nu)mber, (ml. N/10 KOH/ at start 02 .04 03 03 After 18 days--. .02 03 03 04 After 49 days 05 05 05 04 1 Less than .05.

As will be noted in the above table, each of the samples is low in M00 content and has a relatively low acid number. The oxidation stability of the powder on aging is evidenced by the fact that the oxide contents and acid 6 numbers obtained on the samples remain substantially unchanged for a period of almost two months in spite of exposure to the atmosphere when put into sealed jars and opened and stirred for each sampling.

EXAMPLE III Average Nominal Analysis of Product Residual oil content percent.... 1.3 Water content do 0.06 Acid number 0.09 M00 content "percent-.. 0.04

While it will be apparent that the preferred embodiments herein described are well calculated to fulfill the objects above stated it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and meaning of the subjoined claims.

What is claimed is:

1. The method of preparing a molybdenum disulfide powder which comprises providing a powdered mass of molybdenite concentrate resulting from the flotation proc ess containing from about 1% to about 8% flotation oils, charging said oily powdered mass in a fluid energy reduction mill and entraining the particles in a high velocity fluid of controlled temperature achieving mutual impact between the particles and pulverization thereof and simultaneously reducing the oil content by the action of said mill to a level ranging from .05% up to a level approaching the oil content of said oily powdered mass charged to said mill. I

2. The method of preparing a molybdenum disulfide powder which comprises providing a powdered mass of molybdenite concentrate resulting from the flotation process containing from about 1% to about 8% flotation oils and up to about 16% water, charging said powdered mass in a fluid energy reduction mill and entraining the particles in a high velocity fluid of controlled temperature achieving mutual impact between the particles and pulverization thereof and simultaneously reducing the oil content to a level ranging from .05 up to a level approaching the oil content of said oily powdered mass charged to said mill and reducing the water content to a level less than about .5% by the action of said mill.

3. The method of preparing a molybdenum disulfide powder which comprises providing a powdered mass of molybdenite concentrate resulting from the flotation process containing from about 1% to about 8% flotation oils and up to about 16% water, charging said powdered mass in a fluid energy reduction mill and entraining the particles in a high velocity fluid of controlled temperature achieving mutual impact between the particles and pulverization thereof and simultaneously reducing the oil content to a level ranging from 1% to about 5% and reducing the water content to a level less than about .5% by the action of said mill.

4. The method of preparing a molybdenum disulfide powder which comprises providing a powdered mass of molybdenite concentrate resulting from the flotation process containing from about 1% to about 8% flotation oils and up to about 16% water, said powdered mass having an average particle size ranging from about 10 to about 250 microns, charging said powdered mass in a fluid energy reduction mill and entraining the particles in a high velocity fluid of controlled temperature achieving mutual impact between the particles and pulverization thereof to an average particle size of less than about microns, and simultaneously reducing the oil content to a level ranging from .05% up to a level approaching the oil content of said powdered mass charged to said mill and reducing the water content to a level less than .5% by the action of said mill.

5. The method of preparing a molybdenum disulfide powder which comprises providing a powdered mass of molybdenite concentrate resulting from the flotation process containing from about 4% to about 8% flotation oils and up to about 16% water, said powdered mass having an average particle size ranging from about to about 250 microns, charging said powdered mass in a fluid energy reduction mill and entraining the particles in a high velocity fluid of controlled temperature achieving mutual impact between the particles and pulverization thereof to an average particle size of less than about 5 microns, and simultaneously reducing the oil content to a level ranging from 1% to about 5% and reducing the water content to a level less than .5% by the action of said mill.

6. The method of preparing a molybdenum disulfide powder which comprises providing a powdered mass of molybdenite concentrate resulting from the flotation process containing from about 1% to about 8% flotation oils and up to about 16% water, charging said powdered mass in a fluid energy reduction mill and entraining the particles in a high velocity fluid achieving mutual impact between'the particles-and pulverization thereof and re- 'ducing theoil content to a level ranging from 505% to aboutj5% and reducing the water content to a level less than about .5 by controlling the temperature and volume of-the gaseous fluid'supplied to said mill and by controlling the rate of feed of said powderedmass to said mill.

7. Themethod of preparing a molybdenum disulfide powder which comprises providing a powdered mass of molybdenite concentrate resulting from the flotation processoontaining from about 4% to about 8% flotation oils and up to about 16% water, said powdered mass having an average particle size ranging from about 10 to about 250 microns, charging said powdered mass in a fluid energy reduction mill and entraining the particles in a high velocity fluid achieving mutual impact between the 8 particles thereby reducing said powdered mass to an average particle size'of 'less than about 5 microns, and simultaneously reducing the oil content to a level ranging from .05 to about 5% and reducing the'water content to a level less than about .5% by controlling the volume of the gaseous fluid and the temperature of said gaseous fluid to 'a value ranging from about room temperature to about 750 F. and by controlling the: rate of feed of said powdered mass to said mill.

8. The method of preparing a molybdenum disulfide powder which comprises providing a powdered mass of molybdenite concentrate resulting fromthe flotation proc ess containing frornabout 1% to about' 8% flotation oils and up to about 16% water, drying said powdered mass to remove substantiallyall of said water without materially affecting said flotation oil content or said powdered mass, and thereafter cha'rgingthe drie'd said'powdere'd mass in a fluid energy reduction mill and entrain- 'ing the particles in a high velocity fluid of controlled temperature achieving mutual impact between the [particles and pulverization thereof and simultaneously reducing the oil content by the action of said mill to 'alevel ranging from up to a level approaching the oil content of said powdered mass charged to said mill.

9. The method of preparing a molybdenum disulfide powder which comprises providing a powdered mass of molybdenit'e concentrate resulting from the' flotatio'n'process containing from about 4%. to8%. flotation oils and up to about 16% water, drying the said powdered mass, to remove substantially'all' or, the 'water without materially affecting the oil content of the said'powdered mass, and thereafter charging the. dried-said powdered-massin v a fluid energyireduction'mill and entraining the particles in a high velocity nun 'achievingmutual impact-between the particlsand pmv'er'iz'aaon thereof and simultaneously reducing the oil content to a level ranging from about 1% to about 5% byEontroIIing the volume and temperature of the gaseous fluid supplied to 'said mill and the rate of feed of said powdered mass to said mill.

References Cited in the'file of this patent UNITED STATES PATENTS Kaercher I an. 23, 1 945 

1. THE METHOD OF PREPARING A MOLYBDENUM DISULFIDE POWDER WHICH COMPRISES PROVIDING A POWDERED MASS OF MOLYBDENITE CONCENTRATE RESULTING FROM THE FLOTATION PROCESS CONTAINING FROM ABOUT 1% TO ABOUT 8% FLOTATION OILS, CHARGING SAID OILY POWERED MASS IN A FLUID ENERGY REDUCTION MILL AND ENTRAINING THE PARTICLES IN A HIGH VELOCITY FLUID OF CONTROLLED TEMPERATURE ACHIEVING MUTUAL IMPACT BETWEEN THE PARTICLES AND PULVERIZATION THREROF AND SIMULTANEOUSLY REDUCING THE OIL CONTENT BY THE ACTION OF SAID MILL TO A LEVEL RANGING FROM 05% UP TO A LEVEL APPROACHING THE OIL CONTENT OF SAID OILY POWDERED MASS CHARGED TO SAID MILL. 